The invention relates to arrangements of micromechanical elements, preferably microoptical elements, which are each held by means of spring elements. In this respect, they can be pivoted or also deflected in translation around a rotational axis by the effect of electrostatic forces. Electromagnetic radiation can be incident onto a surface of such microoptical elements and can be reflected from there, with the reflection being able to take place while taking account of the respective pivot angles of microoptical elements to achieve a projection of images or to form patterns for the manufacture of semiconductor structures.
For the deflection of micromechanical elements, electrodes are arranged beneath the micromechanical elements to which a presettable electrical voltage can be applied for pivoting or for deflection in translation. The deflection in this respect takes place in accordance with the respective electrostatic force and the restoring force of the spring elements. With deflected micromechanical elements, they are pivoted or deflected back into their starting position again absent any electrostatic force or with reduced electrostatic force. In these cases, the restoring force of the respective spring elements is therefore greater than the electrostatic force.
Depending on the electrical voltage, an electrostatic force can be applied which is sufficient to pivot a micromechanical element by a specific angle or to deflect it by a specific path, which can e.g. be utilized for a directed reflection of incident electromagnetic radiation. The pivoting around the rotational axis or in translation can also take place in two respectively opposite directions. The most varied images can be projected or patterns formed by corresponding pivoting of a plurality of microoptical elements of an arrangement.
The respective deflection at the desired pivot angle or path depends on the relationship of the restoring force of the spring elements and of the electrostatic force and the latter substantially depends on the electrical voltage difference between the respective micromechanical element and an electrode associated with it. A precise control is desired here to be able to observe the desired pivot angle.
A plurality of such micromechanical elements are usually used in the form of an array arrangement, with the dimensioning of the micromechanical elements being kept as small as possible. More than a million such micromechanical elements can thus be present on a chip. They can be controlled by one or more CMOS circuits which is/are arranged beneath micromechanical elements and respectively individually control the micromechanical elements with the electrodes associated with them.
Such a solution is known from U.S. Pat. No. 5,142,405. In this connection, two respective electrodes which are arranged beneath the microoptical elements are associated with each element, here microoptical element, which reflects electromagnetic radiation at a surface. The microoptical elements are held at two oppositely disposed sides by torsion spring elements which are aligned in the rotational axis around which pivoting should and can be achieved. Gaps through which electromagnetic radiation can be incident up to a substrate on which electrodes are formed are present between microoptical elements.
The individual microoptical elements can then, as already addressed, be pivoted individually by specific angles in the respective direction by control of the electrical voltage at electrodes. Electrical voltages e.g. in the range from approximately 0 to 10 V are used in this connection. An electrical voltage can thus be applied to an electrode which is arranged at a side beneath a microoptical element. The respective other electrode and the microoptical element can be switched free of voltage and can be at ground potential. However, there is also the possibility of supplying an electrical voltage to the microoptical element by means of an electrical current supply to the microoptical element so that an electrostatic force effect can be utilized for a pivoting of the microoptical element in accordance with the respective difference of the electrical voltages between the electrode and the microoptical element which results in the desired pivot angle.
In the prior art, electrodes are generally used which are associated with an individual microoptical element for its deflection.
As already indicated, electromagnetic radiation can also be incident through gaps between micromechanical elements or also a frame and micromechanical elements. This radiation can be incident onto the electrically insulating substrate and result in an electrical charging. The electrical charging increases as a result of cumulative effects over time and impairs the relationship of the effective forces. In this connection, the electrical charging takes place in regions on the substrate which are furthest away from the rotational axis around which a pivoted deflection can take place so that the force effect to be observed brings about an increased torque due to the distance to the rotational axis or to the center of mass and thus the desired force relationship of spring effect and electrostatic effect is influenced considerably. Drifts in the deflection over time thereby occur which have to be compensated in a complex and/or expensive manner or which have to be accepted.
The electromagnetic radiation incident through gaps can also induce photocurrents which can also influence deeper layers of a CMOS structure and in so doing can result in charge losses of a storage capacitor. This again impairs the electrical control of electrodes and/or micromechanical elements, which can result in unwanted changes in the respective deflection of micromechanical elements from defaults.
However, shielding with which an incidence of electromagnetic radiation can be prevented in critical regions is counterproductive since the usable angular range for a pivoting of micromechanical elements would thereby be reduced.